Flame-retarding epoxy resin with an efficient P/N/S-containing flame retardant: Preparation, thermal stability, and flame retardance

To further study the effect of the phosphorus, sulfur, and nitrogen-containing flame retardant on epoxy resin, a DOPO-based phenol derivative 4-[(benzothiazolyl 2-amino)(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl) methyl] phenol namely D-P-A, was successfully synthesized from 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), p-hydroxybenzaldehyde (PHBA), and 2-aminobenzothiazole (ABZ), and used to flame retard epoxy resin (EP). As expected, D-P-A imparted flame retardance to epoxy resin. For example, with 7.5 wt% loading of D-P-A, epoxy thermoset passed a UL-94 V-0 rating, and got a LOI value of 29.6%. Besides, D-P-A played an effective role in inhibiting heat release of EP, that EP/7.5% D-P-A showed a peak of heat release rate (PHRR) of 713 kW/m2 much lower than 1137 kW/m2 of EP. However, it decomposed in advance owing to the lower thermal stability of D-P-A. Finally, through Scanning electron microscopy (SEM), Raman spectra and X-ray photoelectron spectroscopy (XPS) and pyrolysis-gas chromatograph/mass spectrometer (Py-GC/MS), it disclosed that D-P-A exerted its flame-retardant activity both in the vapor and condensed phase.